Kim Ramchen was handed a 15-month prison sentence in Melbourne Magistrates Court on Monday after admitting intentionally causing injury, assault with a weapon and unlawful assault over the December 2 stabbing at Keysborough College.
But he could be out of jail on parole as soon as August after already serving 160 days of his eight-month and 14-day non-parole period in pre-sentence detention.
The attack left the school's principal Aaron Sykes, who has not worked since, with multiple injuries.
Mr Sykes would not comment on the legal outcome or process but described his ordeal and thanked those who rushed to his aid.
"Their courage and professionalism in an extremely difficult situation were extraordinary," he said in a statement.
"A member of our library team provided immediate first aid, an assistant principal intervened to assist, and a member of our business team placed herself in harm's way to protect others."
Ramchen appeared in court on Monday via video link in a green prison tracksuit and stared straight ahead throughout sentencing.
On the day of the attack, he had armed himself with a 10cm knife from the school's kitchen after marking the class roll before barging into Mr Sykes' office and aggressively aiming the knife at the principal's neck.
Assistant principal Matthew Sloan, who came from down the hall after hearing shouting from Mr Sykes' office, pulled Ramchen out of the room.
The IT teacher walked off before the school was placed into lockdown, but soon returned with a larger chef's knife, punching Mr Sykes and holding the blade to his face and neck on the ground.
Mr Sykes experienced an adrenaline rush and pushed Ramchen off before his deputy pulled the teacher away and tackled him to the ground.
It took several staff to subdue him until emergency crews arrived.
Mr Sykes escaped the office and was rushed to hospital covered in blood with cuts to his jaw, face, lip and forearm.
Mr Sloan suffered cuts to his ear, cheek, jaw and ribs.
In a police interview, the former IT teacher said he had "mentally snapped" and intended to just incapacitate the principal.
Ramchen's "unwarranted" offending was serious given it occurred in a school environment with students on campus, magistrate Timothy Bourke said on Monday.
"The offending has occurred in what should only ever be a safe place not just for students, but co-workers and the broader school community," he said.
"But for the bravery of Mr Sloan, this could have been a far worse outcome for Mr Sykes."
Defence barrister Amelia Beech previously said Ramchen had been in the midst of a "catastrophic mental health crisis" culminating from a dysfunctional childhood, challenging adulthood, stressful parenthood and undiagnosed mental ill health.
Ramchen has been diagnosed with autism, depressive disorders and anxious distress, which a forensic psychiatrist has found was "causally connected" to the offending, Ms Beech said.
At the time of the attack, his marriage was falling apart and he was unable to understand why his contract was not renewed, the defence said.
The 37-year-old is the son of former Price Is Right host Jacqui Ramchen, who disappeared in 1992.
His late father was charged over her killing until a magistrate found there was not enough evidence to commit him to trial.
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